Threaded Muzzle, Calfee

The question of whether threading the muzzle will distort the bore is again one of those things that can easily be determined by calculation. (I know! this is "book stuff" and many shooters just don't believe it.) For example if the bore should be stressed as high as 60000 psi in compression (which would probably be very high.) and you machined enough material off the O. D. to drop the bore stress down to 30000 psi, you would cause the bore to increase by .00026. This would occur only right at the crown. Back where the threads end along the barrel the increase would be less, down to almost zero. This means the barrel becomes blunderbuss shaped. All agree this affects accuracy.

All this depends on size of the barrel, who much you machine from the barrel, and how high the compressive stresses are in the bore. Any way, you can put your own numbers in and with a little calculation come up with whether or not you think machining the O. D. will hurt. This is not rocket science!
 
Pacecil,

Since you are the man with the calculator and the equation.

If the muzzle pressure is say 10,000 PSI and a 0.900 barrel is machined to 0.850 what expansion of the muzzle will happen when the bullets is about to exit ?

Will there be an expansion with just the machining and no internal pressure ?

What if you then go and put a steel sleeve over that cut that replaces the barrel diameter that was removed and increases it to 0.950, then what ??
 
Paceil

Is there any of this stress in a cut rifled barrel.??.
The reason I ask is Krieger profiles their barrels after all machining operations. When you turn a barrel down to Sporter or LV profile from a 1.200 major diameter, that is a lot of metal removed.
Krieger says that the internal dimensions do not change. They say they can measure within .0001. The lapping that they do is for finish, not dimension.
Of course, the manufactuers of buttoned barrels say pretty much the same. The men at Shilen told me that they do profile barrels after they are finished. They do lap to find tight spots that are present due to the buttoning proccess, but these are quite small, probably .0001 or less, and are located at random in the barrel......jackie
 
Last edited:
In October of last year I toured Shilen, They profile after rifling, but before the lapping process. I would suspect you would have to start with a straight barrel to pull/push the rifling button through to get a consistant bore.

I'm no machinist or specalist in anything...just remember what they told us on the tour.

Charlie
 
Jackie,
Some time ago, I was told that Krieger contours BEFORE drilling. I was skeptical and called them and it checked out....(long time ago....imperfect memory)

The interior dimensions of a buttoned barrel is related to the diameter of the barrel at any particular point at the time that the rifling is formed. To keep the bore uniform, they are buttoned as cylinders, stress relieved to minimize bore change from contouring, contoured, and then lapped.....I think.
 
here is pic of my threaded ,finished brake /tuner assm.

also the group it shot at 1000yds with this threaded tuner,with 2 different loads,the wind was from the left ,can you guess which 2 bullets were slower.the total weight in front of the muzzle ended up being aprox 9.5 oz ,with 3 ozs being adjustable. this barrel has never shot this small before much less with 2 different loads.this tuner is as rigid as the barrel. tim in tx
 

Attachments

  • MVC-002S.jpg
    MVC-002S.jpg
    27.4 KB · Views: 270
  • MVC-003S.jpg
    MVC-003S.jpg
    23.8 KB · Views: 247
Last edited by a moderator:
From Calfee

Thought this post by Calfee on the rimfire forum was interesting: My friends:, Calfee

--------------------------------------------------------------------------------

My friends:

Been working with the centerfre folks.......they've found a new product to increase accuracy.....they call it a muzzle "tuner" I think.....what ever that is?
 
From Precision Shooting

Bartlein Barrels.
A rough blank is first drilled and then contoured to the desired contour.After contouring the blank is then reamed and then pre-lapped before rifling to remove virtually all tool marks.After pre-lapping the barrel is then rifle and finish lapped.
Lynn
 
Friend MatthewKeller

Friend Matthew:

I quote you:

"if someone were to have a barrel threaded BEFORE the bore is finished, than perhaps it would be OK???"

My friend, an excellent observation.....technically, this would result in no loss of accuracy.......due to the bore distortion from threading the muzzle of a finished bore....

This is why barrel makers profile their balnks and then finish the bore (final lap) (button rifled barrels) A cut rifle barrel maker can drill, profile, then ream, rifle and lap.......some may do this?

From a practical standpoint it would be tough for a barrel maker to thread his muzzle, then final lap, successfully, becuase the correct location for the crown may, or may not be, at his threaded muzzle.....

See my friend, if we expect consistant performance from our barrels we must slug and evaluate the bore very carefully to determine the correct location to crown and chamber the barrel........if it were determined the crown needed to be back of the thread the barrel maker put on the barrel, of course we'd be right back where we started...

But again my friend, you made an excellent observation.......

Your friend, Bill Calfee
 
Simply removing material from the o. d. will not change the i. d. - there must be STRESS in the bore that causes it to change. Compressive stress is normally left in the bore after it is bored and rifled. When compressive stress is left in the bore there is at the same time tension stress produced in the o.d. It's the removal of this material in tension on the o. d. that causes a lowering of the compressive stress in the i.d. that causes the i. d. to grow larger.

To BJS6,
If you apply 10000 psi to the bore of a .90 x .24 barrel, the tension stress in the bore goes up to 11531 psi and it will grow .000092".
If you apply 10000 psi to the bore of a .85 x .24 barrel it will grow .000094".
If you apply 10000 psi to the bore of a .95 x .24 barrel it will grow .000091".

As pointed out above there is no change in shape of a barrel when it is machined unless there is stress introduced into the steel either before or after you machine it. This is just a fundamental law - material does not change shape unless you stress it.
 
pacecil said:
Simply removing material from the o. d. will not change the i. d. - there must be STRESS in the bore that causes it to change. Compressive stress is normally left in the bore after it is bored and rifled. When compressive stress is left in the bore there is at the same time tension stress produced in the o.d. It's the removal of this material in tension on the o. d. that causes a lowering of the compressive stress in the i.d. that causes the i. d. to grow larger.

To BJS6,
If you apply 10000 psi to the bore of a .90 x .24 barrel, the tension stress in the bore goes up to 11531 psi and it will grow .000092".
If you apply 10000 psi to the bore of a .85 x .24 barrel it will grow .000094".
If you apply 10000 psi to the bore of a .95 x .24 barrel it will grow .000091".

As pointed out above there is no change in shape of a barrel when it is machined unless there is stress introduced into the steel either before or after you machine it. This is just a fundamental law - material does not change shape unless you stress it.
Click to expand...

Thank you pacecil.

So, if we turned an unstressed barrel from .95 O.D. to .90 O.D., and applied 10,000 psi to the bore of each, the difference in growth between the two would be approximately .000001" (.000091" and .000092")?

Assuming I didn't muck up the calculations, would that .000001" difference be the difference at the muzzle (aka, crown), at cut end distal to the muzzle, or would it be uniform from the muzzle to the distal end of the cut. I'm simply asking because in an earlier post, you stated, "This would occur only right at the crown. Back where the threads end along the barrel the increase would be less, down to almost zero. This means the barrel becomes blunderbuss shaped."

Please don't take this the wrong way, I agree with what you've posted. I understand your explanation regarding the blunderbuss. I've gotten what I believe to be an undeserved rep for being a ball buster in these posts, and can assure you that is not my intention. I just want to clarify where the "growth" you calculated would be occurring. Thanks.
 
Last edited by a moderator:
Pacecil

Krieger says that the cut rifled proccess they employ induces no ID stress in the barrel. In your opinion, how much does the bore of a typical Krieger change when I turn .010 off the OD for 2 inches length, and then put a 36 tpi on that turned spot??........jackie
 
IF threading.......

.....for 2"s to attach a muzzle device will change the ID bore, what does four 18" long "Flutes" do to the barrel?
 
Jan said:
.....for 2"s to attach a muzzle device will change the ID bore, what does four 18" long "Flutes" do to the barrel?
Click to expand...

Jan you can get a feel (literally) of the effect of barrel fluting by pushing a short (1/4" or so) lead slug through a fluted barrel. What effect does fluting have on the felt bore distortion, apparently very little. Skippy Otto fluted a bunch of barrels for himself and others. He also won a bunch with these fluted barrels.
 
You must log in or register to reply here.
Back
Top